Autotrophic starch production by Chlamydomonas species

Microalgal autotrophic cultures may be used as starch feedstocks for a wide spectrum of food and non-food applications, starch-based plastics production included. Chlamydomonas is known to accumulate carbohydrates, but only Chlamydomonas reinhardtii is widely studied. This is the first paper that analyzes the starch content and production rate of four non-conventional Chlamydomonas species and compares their performances to the benchmark C. reinhardtii. Two culture systems—shaken flasks and inclined bubble column (IBC) photobioreactors—and nitrogen depletion conditions were characterized. The irradiance was set at 95 μmol photons m−2 s−1 for flask system and at 220 μmol photons m−2 s−1 for photobioreactors. CO2 and light depletion in shaken flasks strongly affected growth rate and starch production. Under these limiting condition, Chlamydomonas applanata had the best starch productivity of 1.2 mg L−1 day−1. In IBC photobioreactors, the microalgal growth rate and starch production improved with respect to the flask system and nitrogen depletion promoted starch accumulation. The best results of starch productivity and maximum starch fraction were 53 mg L−1 day−1 and 45%DW for Chlamydomonas oblonga and Chlamydomonas moewusii, respectively. This was 49 % more than the studied benchmark. A fast and simple method for starch localization in the microalgal cells was also proposed. The starch granules surrounded the pyrenoid under the growth phase, while they fill the whole cell under nutrient depletion.